Antileukemic activities of human bone marrow and blood cells after culture in interleukins-2, -7 and -12

Acute myeloid leukemia (AML) can be treated by chemotherapy alone, allogeneic bone marrow transplantation (BMT) or autologous BMT. There is a risk of disease recurrence with all these methods, the lowest being associated with allogeneic BMT due to an allogeneic antileukemic effect. Despite its benefits, the use of autologous BMT is limited by high relapse rates due to the persistence of leukemic stem cells in the autologous bone marrow (BM) and/or residual disease in the patient. Thus, it would be desirable to develop methods to decrease relapse rates associated with autologous BMT to a level similar to those of allogeneic BMT. Since individuals who receive BM from a twin are subject to a high risk of relapse, an active immune component that contributes to the elimination of residual disease must be present in the allogeneic BM graft. This project is based on the hypothesis that this can also be achieved by appropriate cytokine manipulation of the antiproliferative activity of autologous effector cells. The natural killer (NK) cell population is the first cell subpopulation to reconstitute after BMT and it is, therefore, an obvious candidate for such manipulations. BMT involving interleukin (IL)-2-activated autologous BM is associated with delayed neutrophil and platelet recovery which can be hastened by the addition of peripheral blood stem cells with the BM. Recent studies with IL-7 and IL-12 suggest that they might mimic or enhance the cytotoxic and antiproliferative activities of IL-2. The effects of these cytokines on bone marrow cells (BMC) and peripheral blood mononuclear cells (PBMC) were compared in a model system in order to assess potential alternate strategies for the ex vivo purging of leukemic cells from human BMC and PBMC. The cytotoxie activity of BMC and PBMC was measured with ⁵¹Cr release assays. The cytotoxic activity exerted by BMC stimulated with optimal doses of IL-2 was less than that of PBMC. While neither IL-7 nor IL- 12 induced cytotoxic activity in BMC, activity was detected in PBMC stimulated with these cytokines. The cytotoxic activity induced by optimal doses of IL-2 in BMC was not enhanced by IL-7 whereas enhancement was observed with IL-12. In contrast, IL-2-induced cytotoxic activity in PBMC was increased by both IL-7 and IL-12 when suboptimal doses of IL-2 were used. BMC and PBMC were cocultured with K562neor cells and their ability to inhibit leukemic cell survival was measured using an assay to detect clonogenic K562 cells. IL-2- stimulated BMC and PBMC inhibited leukemic cell growth in a manner dependent on the initial number of leukemic cells in the coculture. IL-2-stimulated BMC and PBMC were the most efficient in eliminating leukemic cells from the coculture compared to those stimulated with IL-7 or IL-12. IL-7 did not enhance IL-2-induced inhibitory activity on leukemic cell growth in BMC and PBMC while IL-12 did. There was no difference in BMC-mediated inhibitory activity on leukemic cell growth upon cytokine stimulation when tested after 2, 4, 6, and 8 days of culture. IL-7 did not hasten the development of maximal IL-2-induced inhibitory activity relative to IL-2 alone while IL-12 did. Overall, PBMC mediated inhibitory activity on leukemic cell survival in cocultures with K562-neo’ cells was significantly greater and faster than that observed in BMC cocultures when equal numbers of leukemic cells were initially present. These findings suggest that the use of cytokine combinations may have potential in the clinical setting. The information regarding the relative capacities of BMC and PBMC in terms of their antileukemic activities obtained in these experiments will aid in refining the in vitro culture system for these cells such that their antileukemic activity may be optimized.Medicine, Faculty ofPathology and Laboratory Medicine, Department ofGraduat